On the video “Google I/O 2012 - Ten Things Game Developers Should Know”, they talk a bit about a correct way of implementing IAP, but I didnt really follow the explanation. On the IAP docs they dont seem to touch the same topic mentioned on the video, nor on the sample app.
I think that video is about Version 2 of the In-App Billing API, which is much more complicated. You’re probably looking at the docs of Version 3, which was introduced six months after Google I/O 2012, and doesn’t suffer from the issues touched on in the video.